Although in the UK one often finds ordinary horizontal and horizontal/vertical millers badged as being made by Bridgeport these were actually manufactured by Adcock and Shipley, a company owned at one time by Bridgeport and responsible for producing copies of the "real American Bridgeport turret miller" in their Leicester and other factories. Today the original form of the turret miller is, to distinguish it from later computer-controlled and larger models, referred to as the "Series 1". It was first manufactured in 1938 by two immigrant Swedish engineers Magnus Wahlstrom, a toolmaker, and Rudolf F. Bannow (died 1962), a pattern maker and radio ham. The two men had first met in 1928 when Wahlstrom had called to buy wooden loudspeaker parts from Bannow, then president of the "Bridgeport Pattern and Model Works". By 1929 they were in business together and attempting to develop an electrically-powered hedge clipper; however, when this idea was abandoned they began work on a vertical-milling attachment designed to fasten to almost any of the hundreds of thousands of plain horizontal millers then in use. The accessory, which become known as the "Master Milling Attachment", was originally designated by the partners as their "Model C". Smartly presented with a polished aluminium housing, it was well engineered and equipped with a heat-treated and ground spindle running in four precision, pre-loaded bearings (with those at the pulley end allowed to "float" to accommodate expansion and contraction of the spindle) and with a quill that accepted (as standard) 3-inch long B-3 collets. The head was powered by a 1/4 hp motor that gave, in conjunction with 6-step aluminium pulleys, speeds of 465, 675, 1000, 1500, 2140 and 4250 rpm. The first production example was delivered in 1932 to the 'Atlas Tool' company of Bridgeport and the head continued in production long enough to become known as the "Model M" when eventually fitted, some years later, to the first Bridgeport milling machine. The partners, however, were not alone in the conversion market and by the 1940s many similar attachments were available the better-known of which were the "Tree" from Racine, the "Halco" from Detroit and Kearney & Trecker with their Dalrae-manufactured "Midgetmill" and "Speedmill" units.
One special version of the Bridgeport Model C was made for use on precision Hardinge horizontal millers (early versions were badged Cataract MD5) and these heads can be recognised by a Serial numbers beginning with the letter "H". Although identical (at a glance) to the standard Model C they were not as long and used a shorter "2VB" Collet closer. From the centre of the mounting holes to the bottom of the 2VB collet closer was 5 3/16" whilst the same dimension on the B-3 collet closer model was 611/16". 
By 1936 the original head been improved by the addition of a 1/2 hp motor, the inclusion of a sliding quill with 3.5" of travel - which of course radically improved the unit's drilling and boring performance - a choice of either No. 2 Morse or No. 7 Brown & Sharpe taper and an improved speed range that ran through 275, 425, 700, 1050, 2100 and 4250 rpm. With this much more useful specification business began to pick up and, by 1938, with sales of 500 units per annum, and seeking further expansion, the partners decided to incorporated the head in a completely new design of highly-versatile milling machine that they would produce themselves - the Bridgeport. In true tradition the initial sketches were said to have been drawn by Rudy Bannow on a paper bag whilst waiting to unload patterns at a customer's works. In 1938 the Company changed its name to "Bridgeport Machine Inc." and in August of that year the first Bridgeport turret milling machine was completed and shipped to the plant of the Precision Die Casting Company of Syracuse, New York - this first example, invoiced at $995, was later recovered by Bridgeport and donated to the Henry Ford Museum at Dearborn, Michigan. Today it can be found at the Precision Museum in Windsor, Vermont, U.S.A.
Because the Bridgeport was extremely well thought out its versatility was quickly appreciated in both toolrooms and production plants; not only did the whole upper turret pivot on the main column, but the round horizontal ram (driven by a rack and pinion on some but not all versions) could be moved forwards and backwards over a distance of 12 inches; once that setting was achieved the whole assembly could then, if needed, be swung left and right as well and the head tilted over under the control of a large worm-and-wheel gear - the latter arrangement ensuring the alterations was made quickly and with great precision. The value the value of this latter feature can only be truly appreciated if you have ever have struggled to hold 75 lbs of cast iron in one hand - over at an angle in perfect alignment with an engraved mark - whilst simultaneously trying to tighten a miserably-small nut buried in some dark and oily recess hidden away at the back of the machine. Probably due to difficulties with rigidity not all models had a clevis end on the vertical-head end of the ram, later types were offered with a more robust flat fitting but retaining a clevis at the other end to mount a slotting attachment. These early models had a 5-inch diameter round horizontal ram, distinctly different to the "square" type that was available from September 15th, 1952; this later ram, and its mounting, could be used on earlier machines and was advertised for a time by the factory as a conversion unit. With the new design the rigidity of the ram had been sufficiently increased to allow the reintroduction of a clevis end for the vertical head (like that the competing Cross miller) that once again allowed it to be "nodded" up and down through an angle of 45 degrees each side of vertical. As an interesting aside some early (round-ram) machines have been found with a Type C head having an improved quill travel of 5 inches rather than the usual 3.5".
Continued below: